We have isolated clonal cell lines that show traits of human retinal progenitor cells. The cells are derived from retinoblastoma tumors. While the tumor cells are mutant in the R81 gene, the progenitors do not show mutations (unless inherently carried in the genome). Studies proposed here deal with fully wildtype monoclonal cell lines. To fully qualify as retinal progenitors, the cells must be self renewing, must show markers of progenitor cells, and must show the potential to differentiate into retinal cells. Preliminary studies show that these cells are self renewing, express markers characteristic of neural, retinal progenitor cells and assume morphological traits of retinal cells upon transplantation. Our objective here is (1) to obtain evidence that these cells have the capacity to differentiate into functional retinal cells. Studies are proposed to subject the cell lines to environments that will provoke their differentiation, including altering growth factors in culture media, reaggregation culture with embryonic or postnatal rat retinal cells, introduction of cells into early postnatal rat or mouse retinal explants, and transplantation of cells into developing postnatal rat retina. Progenitor cells will be marked with enhanced green fluorescent protein and their potential to express retinal markers and develop appropriate morphology of retinal cells will be assessed. In addition, we propose (2) to derive additional cell lines to bank cells for future studies. Fully characterized progenitor cells provide an invaluable resource for the study of retinal differentiation, may provide a resource for cell replacement in degenerated or damaged mammalian retina, and provide a resource for delivery of agents to prevent or repair diseased retina.